1. Field of the Invention
This invention relates to a slide fastener and more particularly to a lockable slider for slide fasteners.
2. Description of the Prior Art
The invention is an improvement on the slider described, illustrated and claimed in the applicant's preceding United States Pat. application (Filed Oct. 28, 1964, Ser. No. 407,199) which has already matured as United States Pat. No. 3,270,535. The slider is of the type comprising a slider body, a cylindrical member rotatably enclosed at the fore thereof and having a slanted annular cam face at its lower surface, a compression coil spring urging the cylindrical member upwardly for enabling the rotation thereof by a separate key, a locking lever pivotally at its middle mounted on the slider body, having its one end held in contact with the slanted annular cam face of the cylindrical member and provided at the other end with a locking pawl, and a separate resilient member, a leaf spring provided at the rear of the slider body urging the locking lever downwardly, so that the locking pawl is brought into locking engagement with interlocking fastener elements in response to the rotation of the cylindrical member.
This type of slider has certainly gained appreciable and valuable advantages that since the locking pawl is not actuated directly by cam motion but is actuated indirectly through a spring force in an extremely natural manner, even if the pawl would come into contact with the tops of fastener elements at the beginning of locking motion, but not proceed into the interspace of fastener elements, the cylindrical member is not prevented from turning continuously by virtue of the resiliency of spring, and when the slider body is moved slightly, the pawl automatically gets into the next interspace of fastener elements to effect the required locking, so that locking mechanism is never subjected to any such compulsive force during locking operation that might damage the parts. In addition, because of the fact the locking pawl is under the resilient restraining force by virtue of spring in the locking position, the slider body can be moved further in the direction of closing the slide fastener, but not in the opposite direction. Consequently, in a travelling bag for example, the key may be inserted into the key holes at any convenient position easy for operation of the key for effecting the locking, and then the key may be withdrawn from the key holes, while the slider body can be moved further in closing direction.
Notwithstanding the advent of these appreciable advantages, the prior art slider is found to have still suffered from various drawbacks which arise from the same cause, the inevitable provision of the additional leaf spring above the locking lever and hence at the rear of the slider body. Firstly, this requires the rear of the slider to become relatively bulky, thereby rendering the slider as a whole unsightly or ugly in appearance. Secondly, the addition of the part makes the assemblage of the lockable slider the more complex, time-consuming and tedious in a natural consequence. This is more so when the part to be added is resilient as is the case in this prior art lockable slider. Thirdly, this entirely precludes the possibility of providing an aperture large enough to loosely receive the pintle or pivotal end of the pull tab thereon for free movement thereof relative to the slider body. Such free movement of the pull tab relative to the slider body is very significant from the standpoint that this type of lockable slider finds its most application to a travelling bag, a brief case and so forth, which articles are likely to be positioned in variable relative positions to the carrier thereof or the man manipulating the lockable slider attached thereto and thus require easy manipulation of the pull tab at any relative position of the manipulator to the pull tab.